Factors Affecting the Rate of Genetic Change

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The equation relating the rate of genetic change resulting from selection to four factors: accuracy of selection, selection intensity, genetic variation, and genetic interval

Accuracy of Selection

"Accuracy of breeding value prediction" a measure of the strength of the relation

Selection Intensity

A measure of how "choosy" breeders are in deciding which individuals are selected.

Genetic Variation

Variability of breeding values within a population for a trait under selection

Generation Interval

The amount of time required to replace one generation with the next. The shorter the generation interval, the faster the rate of genetic change.

Rate of Genetic Change or Response to Selection

The rate of change in the mean breeding value of a population caused by selection.

Accuracy of Selection

The correlation between true breeding values and their predictions for a trait under selection.

Selection Criterion

An EBV, EPD, phenotypic value, or other piece of information forming the basis for selection decisions.

Selection Intensity

The difference between the mean selection criterion of those individuals selected to be parents and the average selection criterion of all potential parents, expressed in standard deviation units.

Selection Differential

The difference between the mean selection criterion of those individuals selected to be parents and the average selection criterion of all potential parents, expressed in units of the selection criterion.

Truncation Selection

Selection on the basis of a distinct division in the selection criterion (point of truncation) above which individuals are kept and below which they are rejected

Proportion Saved (p)

The number of individuals chosen to be parents as a proportion of the number of potential parents

Generation Interval (L)

The average age of parents when their selected offspring are born.

Closed Population

A population that is closed to genetic material from the outside

Genetic Trend

Change in the mean breeding value of a population over time

Phenotypic Selection Differential (S)

The difference between the mean performance of those individuals selected to be parents and the average performance of all potential parents, expressed in units of the trait.

Progeny Test

A test used to help predict an individual's breeding values involving multiple matings of that individual and evaluation of its offspring

Replacement Rate

The rate at which newly selected individuals replace existing parents in a population

Selection Risk

The risk that the true breeding values of replacements will be significantly poorer than expected